and analyzed to determine if structure changes are occurring that indicate pos- 

 sible failure modes and the need to monitor the structure(s) more closely. The 

 jetties at Manasquan Inlet, New Jersey, were nominated for periodic monitoring 

 by the U.S. Army Engineer District, Philadelphia (Philadelphia District). 



Project Location and Brief History 



Manasquan Inlet is located on the Atlantic Coast of New Jersey approxi- 

 mately 42 km (26 miles) 1 south of Sandy Hook and 37 km (23 miles) north of 

 Barnegat Inlet (Figure 1). The inlet provides the northernmost connection 

 between the ocean and the New Jersey Intracoastal Waterway. Reliable surveys 

 as early as 1839 reveal that the inlet has migrated between its present location 

 and 1.6 km (1 mile) north (Philadelphia District 1978). On a number of occa- 

 sions prior to jetty completion in 1931, the inlet closed completely. 



Stabilization of the inlet was first attempted between 1881 and 1883 with the 

 construction of timber jetties. Both these and subsequent timber jetties built in 

 1922 failed, leading to Congressional authorization of the present project layout 

 in 1930. The project involved construction of two rubble jetties, with steel 

 sheet-pile cores, spaced 122 m (400 ft) apart. Built to a crest height of +4.3 m 

 (+14 ft) mean low water (mlw), 2 the jetties extend to the -3-m (-10-ft) contour. 

 The north jetty was 375 m (1,230 ft) long, and the south jetty was 314 m 

 (1,030 ft) in length. Core stone weight ranged from 45.4 to 226.8 kg (100 to 

 500 lb), and 1,814-kg (2-ton) capstone was used for armor. Originally, the 

 authorized channel was 76.2 m (250 ft) wide and 3 m (10 ft) deep between the 

 jetties and 91.4 m (300 ft) in width and 2.4 m (8 ft) in depth for the interior chan- 

 nels. In 1935, the authorized channel depth between the jetties was increased to 

 4.3 m (14 ft) and the interior channel depth to 3.7 m (12 ft). The current project 

 is shown in Figure 2. 



Through the mid-1970s, the jetties were repeatedly damaged by storms and 

 structural settlement (Philadelphia District 1978). Beach erosion north of the 

 inlet and accretion to the south emphasized the impact of the jetties on the lit- 

 toral system. Shoaling of the navigation channel increased as the structures 

 deteriorated and became more permeable. Numerous repairs were attempted, 

 using armor stone of up to 10,890 kg (12 tons), without success. Additional 

 information relative to the repair and rehabilitation history of the jetties can be 

 found in Smith (1988). A 1962 aerial view of the deteriorated jetties is shown in 

 Figure 3. 



A major rehabilitation of the jetties was completed in 1982 and involved the 

 use of 14,515-kg (16-ton) reinforced dolos armor units (Figures 4 and 5). 



' Units of measurement in the text of this report are shown in SI (metric) units, followed by non-SI 

 (British) units in parentheses. In addition, a table of factors for converting non-SI units of 

 measurement used in figures in this report to SI units is presented on page vii. 

 : All elevations (el) and depths cited herein are in meters (feet) referred to mean low water (mlw). 



Chapter 1 Introduction 



